I have this rattle that is driving me crazy! It ONLY happens when accelerating. As soon as I let off the gas it stops. Kinda sounds like a baby rattle or marbles rattling. They have replaced part of my muffler which didn't work and now basically saying "theres nothing they can do about it." I believe it may be the catalytic converter but not sure what to do. What's a warranty there for if they are not willing to work on it. Has anyone had this problem? Any suggestions?